Although this particular outbreak was small – there are over one million Salmonella illnesses every year in the U.S. – it covered a lot of territory. Illnesses were reported in 41 states.

Salmonella is a bacterial infection usually spread through contaminated food or water. Most people who become infected develop diarrhea, fever and stomach cramps. Severe cases can result in death.

Although the CDC investigation did not identify a single, common source of contaminated kratom, it found enough evidence to declare that kratom was the “likely source.”

State and local health officials interviewed 103 people who were sickened in the outbreak and found that 74 percent reported consuming kratom in pills, powder or tea. The kratom was purchased online and from retail locations in several states. Over a dozen brands of kratom were recalled as a result.

“This outbreak investigation is over. However, some kratom products that were contaminated with Salmonella have not yet been recalled and may still be available for purchase or in people’s homes,” the CDC said in a statement. “Salmonella was identified in nearly half of the kratom products tested during this investigation. Eighty-five different DNA fingerprints of Salmonella were identified in samples of kratom products. This information indicates widespread Salmonella contamination in kratom from multiple retailers.”

The CDC has modified a previous recommendation that no one consume kratom “in any form.” The agency now recommends that only people at risk of a Salmonella infection – such as pregnant women, children, older adults, and people with compromised immune systems — avoid consuming kratom products.

“If you are considering using kratom, talk to your health care provider first, especially if you are in a group more likely to get a severe Salmonellainfection,” the CDC said.

Millions of Americans use kratom to treat chronic pain, addiction, depression, anxiety and other medical conditions. Kratom comes from the leaves of a tree that grows in southeast Asia, where it has been used for centuries as a natural pain reliever and stimulant.